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For the past 15 years, satellites that measure the color of the ocean have given us a view

of sea surface phytoplankton which form the base of the food web and half of all the oxygen

we breathe.

These satellite data are being used to understand fish distributions and why some fisheries

suddenly collapse.

In these monthly composites, high amounts of phytoplankton in the ocean are shaded green

to yellow for the most. Water with little to no phytoplankton is dark blue.

Phytoplankton abundance is controlled by the availability of sunlight and nutrients. Winds

over the ocean drive currents away from the coast and equator, creating a void at the

surface that’s filled by nutrient-rich water from the deep ocean upwelling to the sunlit

surface.

Combining satellite data with samples collected from the ocean enables scientists to better

understand where these microscopic plants live and support different ecosystems and

how physical and chemical changes affect them.

Seasonal changes are most obvious. Slower changes are also apparent, one of the largest

being El Nino in the tropical Pacific, with an approximately 5 year cycle. El Nino causes

reduced upwelling, with warmer water and less phytoplankton; its opposite phase is called

La Nina with more phytoplankton than normal.

Since phytoplankton form the base of the food web in the ocean, they impact animals higher

up the chain. A major consequence of El Nino is the loss of commercially important species

from their usual location: anchovies around South America, squid off of California, salmon

around the Pacific, and others. Not only fish are impacted, but animals that

depend upon them such as sea lions, seals and sea birds experience famine.

Understanding El Nino and other natural and man-made causes for fisheries collapse will

guide decisions about how to help them recover.